316 HYDROID^. Part IV. 



with those of the American species, even to the constricted truncate aperture (PI. 

 XXXIV. Fig. 11, h^), but they bear also free medusae. The branches spread 

 nearly at right angles (PI. XXXIII. Firj. 11), and the whole appearance of the 

 hydromedusarium reminds us of that little Caryophyllaceous plant, the Spergularia 

 rubra. In the earlier stages of growth {^Fig. 2) the stem is very simple ; the 

 branches arise, at intervals of about one tenth of an inch, in a spiral, and, in 

 progress of growth, each branch gives off other branches, which are arranged in 

 the same way. Every interval of the chitinous stem, between any two branches, 

 is gently curved ^Fig. 6, [i), and the outlines are parallel ; at the base of each 

 there are four or five i-ings (e) ; and so is it with every branch, whether it 

 be pi'imary, secondary, or tertiary. Each branch pursues a zigzag course, every 

 internode trending at an angle of forty-five degrees from the previous one. 



The pedicels of the hydra calycles {Figs. 6 and 11, C) are ringed (c^), 

 from base to apex, and, when fully developed, are nearly as long as the inter- 

 vals of the branches. Those hydra? which terminate the branches {Fig. 6, C^) 

 are usually not completely developed, at least the pedicels are not as long as 

 the others, and, being in direct continuation with the branches, appear as if par- 

 tially ringed, whereas the smooth portion belongs to the branches proper. The 

 calycle of the stei-ile hydrte varies in shape from a narrow {Fig. 5, c^) to a broadly 

 campanulate {Fig. 12, c^) outline, but its foi-m is more or less dependent vipon the 

 contraction or exj)ansion of the hydra. When the calyx is empty, and left to 

 itself, it assumes a broad campanulate form {Fig. 12). The rim (c'') is even, but 

 polyhedral {Fig. 12"), and each of the twelve sides (e^) is slightly curved inwardly. 

 This peculiar figure is confined to the teniiinal fifth of the cuj), whereas the 

 remaining portion is perfectly circular in outline. At a short distance above the 

 base of the calyx, equal to the height of one of the rings, a semi-partition (c) 

 projects into the cavity of the bell. It is as thick as the wall of the calyx, at 

 its margin, but thins out to a sharp edge at the border of the central hole, which 

 occupies one fourth of its breadth. The cavity thus formed below the semi-par- 

 tition, is half as deep as broad. The wall of the calyx is thin at the base, where 

 it bears the same proportion to the whole that the shell of a foAvl's egg bears 

 to the whole egg, but it thins out gradually to the margin, where it is a mere 

 film, and very frail and flexible. During the breeding season, the reproductive 

 calycles {Fig. 11, A B) occupy the foi-ks of the branches and of the pedicels; 

 each one is borne on a short peduncle, consisting of three or four rings, and, 

 when fully developed, broadens gradually upwards, and, attaining a height double 

 that of the hydra calycle, it suddenly constricts (PI. XXXIV. Fig. 11) to one third 

 of its previous breadth, and then terminates in a slightly expanding short neck 

 (F), which is about as long as two of the rings of the peduncle. The breadth 



